This field of this invention is minimally invasive biological fluid sampling and analyte measurement devices.
The detection of analytes in biological fluids is of ever increasing importance. Analyte detection assays find use in a variety of applications, including clinical laboratory testing, home testing, etc., where the results of such testing play a prominent role in the diagnosis and management of a variety of disease conditions. Common analytes of interest include glucose, e.g., for diabetes management, cholesterol, and the like.
A common technique for collecting a sample of blood for analyte determination is to pierce the skin at least into the subcutaneous layer to access the underlining blood vessels in order to produce localized bleeding on the body surface. The accessed blood is then collected into a small tube for delivery and analyzed by testing equipment, often in the form of a hand-held instrument having a reagent test strip onto which the blood sample is placed. The fingertip is the most frequently used site for this method of blood collection due to the large number of small blood vessels located therein. This method has the significant disadvantage of being very painful because subcutaneous tissue of the fingertip has a large concentration of nerve endings. It is not uncommon for patients who require frequent monitoring of an analyte to avoid having their blood sampled. With diabetics, for example, the failure to frequently measure their glucose level on a prescribed basis results in a lack of information necessary to properly control the level of glucose. Uncontrolled glucose levels can be very dangerous and even life-threatening. This technique of blood sampling also runs the risk of infection and the transmission of disease to the patient, particularly when done on a high-frequency basis. The problems with this technique are exacerbated by the fact that there is a limited amount of skin surface that can be used for the frequent sampling of blood.
To overcome the disadvantages of the above technique and others that are associated with a high degree of pain, certain analyte detection protocols and devices have been developed that use micro-needles or analogous structures to access the interstitial fluid within the skin. The micro-needles are penetrated into the skin to a depth less than the subcutaneous layer so as to minimize the pain felt by the patient. The interstitial fluid is then sampled and tested to determine the concentration of the target constituent. The concentration of a constituent within the interstitial fluid is representative of the concentration of that constituent in other bodily fluids, such as blood. Thus, by sampling interstitial fluid and measuring the level of glucose therein, for example, the corresponding level of glucose in the patient""s blood can be derived.
Despite the work that has already been done in the area of analyte testing, there is a continued interest in the identification of new analyte detection methods that more readily meet the needs of the relevant market. Of particular interest would be the development of a minimally invasive analyte detection system that is practical, manufacturable, accurate, easy to use, as well as safe and efficacious.
RELEVANT LITERATURE
U.S. Patents of interest include: U.S. Pat. Nos. 5,161,532, 5,582,184, 5,746,217, 5,820,570, 5,879,310, 5,879,367, 5,942,102, 6,080,116, 6,083,196, 6,091,975 and 6,162,611. Other patent documents and publications of interest include: WO 97/00441, WO 97/42888, WO 98/00193 WO 98/34541, WO 99/13336, WO 99/27852, WO 99/64580, WO 00/35530, WO 00/45708, WO 00/57177, WO 00/74763 and WO 00/74765A1.
Minimally invasive biological fluid sampling and analyte measurement devices and systems, as well as methods for using the same, are provided. Generally, the subject device includes an elongated sampling means configured to pierce a skin surface to provide access to biological fluid, and concentrically-spaced working and reference electrodes positioned within the elongated sampling means that define an electrochemical cell for measuring the concentration of analyte within the biological fluid. In certain embodiments, the device further includes an insulating material positioned between the concentrically-spaced electrodes. The device also includes means for making an electrochemical measurement of an analyte in the electrochemical cell, e.g., a coulometric, amperometric or potentiometric measurement.
In a more specific embodiment, the subject device is characterized by a piercing member made of coaxially spaced-apart working and reference electrodes that provide for an electrochemical reaction cell, whereby a reaction area or zone is between the electrodes. The electrochemical cell is employed to make an electrochemical measurement of an analyte in a sample of biological fluid that has been accessed by the piercing member and transported into the electrochemical cell. A porous material is positioned in the space between the electrodes to define the reaction area or zone, that acts to optimally position the electrodes with respect to each other, usually in a parallel configuration. The porous material comprises a plurality of pores that exert a capillary action on the sampled fluid, causing the fluid to be drawn into the porous material.
An exemplary method of the subject invention involves using at least one subject micro-needle having an open distal end and an electrochemical cell therein. The electrochemical cell may further include a redox reagent system and a concentrically-layered electrode configuration, e.g., coaxially working and reference electrodes. The micro-needle is inserted into the skin to a selected depth, preferably to a depth that avoids contacting nerve endings and blood vessels. Next, the sample of biological fluid present at the open distal end of the micro-needle is then wicked, by means of a capillary force, into the electrochemical cell. An electrochemical measurement is then made between the working and reference electrodes, where such a measurement provides an electrical signal that is representative of the concentration the constituent in the sample. The concentration of the constituent in the patient""s blood is then derived from the obtained electrical signal. A numerical value representing this concentration may then be displayed on a display unit. A software algorithm that is part of the device, e.g., programmed into the control unit present in the device, may be employed to determine the signal levels transmitted by the control unit to the cell and for deriving the concentration level of the target analyte.
In some embodiments, the subject invention includes a system characterized by one or more devices, each in the form of a micro-piercing member, a control unit, a display unit and a housing. Also provided by the subject inventions are kits for use in practicing the methods of the subject invention.
The subject devices, systems, methods and kits find use in analyte concentration measurement of a variety of analytes and are particularly suited for use in the measurement of glucose concentration in interstitial fluid.